The invention relates generally to venting units for venting air from a rubber article forming mold and, more specifically, to venting units having a yieldable valve element for venting air from a tire mold.
In the forming of vehicle tires, it is desirable that the tire side wall be free of any projected rubber pins, impressions, depressions, or other surface irregularities. The forming of the pins or needles is usually the result of the uncured tire band, in the final forming operation of the tire, being forced into the air release vents or passages which have terminal ends open to the inner surface of the tire forming cavity of the mold. For economical purposes, the pins are not removed and thus give to the tire an unfinished or hairy appearance.
A number of attempts have been made to avoid surface irregularities on the tire side wall by the use of valve units. In British Pat. No. 922,788, issued Apr. 3, 1963, a valve body is movably mounted in a vent for movement to a vent closing position by the expansion of the band against the cavity side wall.
The release of air from the mold cavity through vents in U.S. Pat. No. 3,842,150, is controlled by valves that are actuated in response to a selective application of pressure on the valves. Appreciable time and expense is involved in the manufacture of the valves and in the control system for synchronizing the flow of variable pressure air through the valves with the steps in the tire forming operation.
In U.S. Pat. No. 4,492,554, the venting unit for the tire mold is engaged and moved by an expanding tire band to a vent closing position to form a smooth surface continuous with the inner surface of the tire forming cavity and is yieldably urged to a vent opening position by a spring means. Frequent cleaning of the venting units, however, is required to ensure their proper operation resulting in down time losses of the molding equipment.